In most disk drives, a representative example of which is the hard disk drive, a head reads or writes data on or from a disk used as a recording medium, while it is flying above the disk. The flying height of the head influences the data recording and reproducing characteristic of the disk drive, and should therefore be set to an optimal value.
In order to set the flying height of the head to an optimal value, a technique may be used which first measures the head flying height and then adjusts the head flying height in accordance with the value measured. A method of adjusting the head flying height is known, which heats the slider holding the read/write element of the head, thereby controlling the flying height. On the other hand, a method of measuring the flying height is known, which reads data from the disk and uses the harmonic component contained in the data, thereby measuring the flying height of the head (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2008-192244).
The method that utilizes the harmonic component can dynamically measure the head flying height. If this measuring method is used in combination with the method of heating the slider, the head flying height can be dynamically set to an optimal value. The head flying height may change due to, for example, the ambient temperature of the head. In any common hard disk drive, the heating of the slider is controlled by changing the amount of heat to be applied to the slider from the value that has been set, during the manufacture of the disk drive, in accordance with various use conditions (including the ambient temperature of the head).
However, the disk drive manufactured in and shipped from the factory may be used in conditions that differ from those considered during the manufacture. Consequently, the head will possibly fail, in some cases, to have a flying height optimal to the conditions in which the hard disk is actually used, even if the preset amount of heat is applied to the slider.